The present invention relates to the art of processing digital images. More particularly, the present invention relates to the art of image filtering techniques for visual enhancement of digital prints and photographs.
Many techniques exist for processing and filtering signals, especially signals representing two-dimensional (2D) images. As the 2D images are increasingly digitized and computerized, it becomes easier to apply many more different filtering techniques than before. Digitized images are typically represented by an array (typically but not necessarily rectangular) of pixels, each pixel represented by a digital value and representing a smallest unit of the digital image.
Spatial filtering is the filtering of an image in the spatial domain. That is, the value of each pixel of the image is modified in contextual relationship to neighboring pixels. Typically, spatial filtering is used to remove noise, to enhance the image, to manipulate the image into some more visually attractive form, or any combination of these. For example, a low pass filter, applied to an image, smoothes the image by removing finer details such as noise but will also blur image detail.
On the other hand, a high pass filter removes low spatial frequencies while retaining (xe2x80x9cpassingxe2x80x9d) high frequency information. This tends to highlight edges and other sharp boundaries. Because of human visual perception consideration, an image having enhanced high frequency components appears sharper than an image without enhanced high frequency components. The following is a typical high pass filter in a 3xc3x973 (conservative) kernel: 
Filters are not limited to 3xc3x973 in size, and the values of each component of the kernel may be different to achieve different filtering effects. However, because such filters are rectangular in configuration, they tend to amplify the grid-nature, or digital-ness, of the image they are filtering.
Further, filters of this nature are not necessarily matched in either scale (or strength) or spatial extent to the natural visual scale that is optimum for viewing the digital form of the image.
Consequently, there is a need for a technique and apparatus for filtering images overcoming these shortcomings of the current art and matching the digital image in scale and extent to the optimum visual characteristics as viewed.
The need is met by the present invention. According to one aspect of the present invention, a method of processing an image includes spatially filtering the image using an adaptive convolution filter.
According to another aspect of the invention, an apparatus for processing an image includes a processor and storage connected to the processor. The storage includes instructions for the processor to filter the image using an adaptive convolution filter.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in combination with the accompanying drawings, illustrating by way of example the principles of the invention.